3-Φ phase reversal detection logic

[khatus]

hello guys this the flow chart for 3-Φ phase reversal detection.My question is why they use the logic

if captured time(T) in between 3 mesc and 8 msec
Is that for (3+8)/2 = 5.5 msec??

It is not clear to me.

In my country the frequency is 50Hz so what should i take??
Can i take 4msec and 9.32 msec?? So that (4+9.32)/2 gives 6.66 msec??

[ledtester]

Let's consider a 60 Hz system.

In one direction the time between the L2 and L3 zero-crossings will be close to 5.5ms.

In the opposite direction the time will be 16.66 - 5.5ms = about 11ms.

So if you allow a 3 to 8 ms window you will comfortably discriminate between the phases going one way versus the opposite way.

For 50 Hz the times are 6.66ms vs. 20ms - 6.66 = 13.3ms. Again, the 3 to 8 ms window allows for some variance in timing while still giving a large margin for telling the difference between the forward and reverse modes.